With respect to spin-valve films that are applied to magnetic devices such as magnetic heads and MRAMs (magnetic random access memories), TMR (tunneling magnetoresistance) elements and CPP (current-perpendicular-to-plane)-GMR (giant magnetoresistance) elements, in which a sense current is supplied in a direction approximately perpendicularly to a film plane, are paid attentions since they can exhibit a large MR.
On the other hand, in recent years, it has been observed that a magnetoresistance effect with a high magnetoresistance change rate can be resultant by using a nanocontact between Ni thin wires. See Phys. Rev. Lett. 82 2923 (1999).
Furthermore, development of a magnetoresistive element in which a magnetic nanocontact is extended to a three-dimensional structure is in progress. See JP-A 2003-204095 (KOKAI).
The magnetoresistance effects described in the above-mentioned documents are exserted in relation to that twisting of magnetization, i.e., a magnetic wall is generated in a magnetic nanocontact when the magnetization directions of a pinned layer and a free layer are in antiparallel. It is considered that this magnetoresistance effect increases more as the magnetization in the magnetic nanocontact changes more rapidly, i.e., as the thickness of the magnetic wall (magnetic wall width) that is generated in the magnetic nanocontact is narrower. In addition, since a magnetic wall width depends on the diameter of the magnetic nanocontact, a smaller diameter of the magnetic nanocontact is preferable. Furthermore, it is desirable that the purity of a magnetic metal in the magnetic nanocontact, i.e., magnetic wall, is high.
However, it is very difficult to form a magnetic nanocontact having a small diameter and comprising a magnetic metal at a high purity. Furthermore, since the magnetic nanocontact is formed of a ferromagnetic metal, there is a fear that a interlayer coupling field between the pinned layer and the free layer increases, thereby an operation point as a read head shifts toward a higher magnetic field.